SAN DIEGO, California (CNN) -- More than 100 homes in an upscale San Diego community were evacuated after a landslide about 60 yards wide pulled the earth from beneath a three-lane road and some of the multimillion-dollar homes that adorn it.

Gina Yarbrough sent this picture of the road that collapsed in Wednesday's landslide.

Mayor Jerry Sanders declared a state of emergency, asking California and the federal government to help the La Jolla community recover from the Wednesday landslide. As of Thursday morning, he had already received offers of aid from legislators, the governor's office and the White House, he said.

Officials warned for at least two weeks that the ground was shifting beneath the hillside community along Soledad Mountain Road.

Holes were drilled into the unsettled hillside to investigate the cause and magnitude of the shift, which earlier ruptured a water line, and according to some media reports, began cracking Soledad Mountain Road in July.

At least 111 homes were evacuated, but Sanders said residents would be allowed to return to 75 of those houses by early Thursday morning. Several homes were damaged and at least one was destroyed, according to media reports.

Nine homes are "red tagged," meaning no one is allowed to enter them, and 27 more are "yellow tagged," which means residents can return for necessities, but cannot stay, Sanders said.

According to the San Diego Union-Tribune, the landslide downed power lines and caused a minor gas leak. More than 2,400 customers were briefly left without electricity, but most residents had their power restored by Thursday, KGTV reported. The Red Cross opened a shelter at La Jolla High School.

Deputy city engineer Robert Hawk told the Union-Tribune that the hillside has slowly been slipping for years because the soil is unstable. Landslide incidents in the neighborhood date back to the 1960s, Hawk told the newspaper.

Pat Abbott, a retired geological sciences professor at San Diego State University, told the Union-Tribune that Mount Soledad is made up of weak layers of rock and that the culprit in the landslide is nature.

"Gravity pulling on the incline is pulling down masses of earth and those masses of earth have houses on top of them," Abbott told the paper. "It's a geologically bad site and should not have been built on to begin with."E-mail to a friend